The present invention relates to a mechanical constant estimating device for estimating a mechanical constant such as an inertial moment in a drive machine such as a machine tool or a robot employing an actuator such as a motor.
To control a drive machine such as a machine tool or a robot employing an actuator such as a motor at high precision and stably, it is required to estimate the mechanical constant such as an inertial moment for the drive machine correctly.
FIG. 6 is a block diagram of a velocity control system containing a conventional mechanical constant estimating device, which has the configuration equivalent to that of a control device for an electric motor servo system having an auto-tuning function capable of setting the convergence of control gain as described in JP-A-11-313495.
In FIG. 6, reference numeral 30 denotes a torque command generating portion for generating a torque command xcfx84r based on a velocity command (not shown), 31 denotes an actuator such as a motor for generating a drive torque xcfx84m in accordance with the torque command xcfx84r, 32 denotes a drive machine that is driven by the actuator 31, 33 denotes a velocity detector for detecting a machine velocity vm of the drive machine 32, and 34 denotes a mechanical constant estimating device for estimating an inertial moment estimated value Je by inputting the machine velocity vm and the torque command xcfx84r. Reference symbol xcfx84d denotes a disturbance torque applied to the drive machine 32.
Also, the torque command generating portion 30 alters the internal constant such as a gain (auto-tuning), based on the inertial moment estimated value Je output from the mechanical constant estimating portion 34, and generates the torque command xcfx84r in accordance with the inertial moment estimated value Je.
FIG. 7 is a block diagram showing the configuration of a conventional mechanical constant estimating device, which is equivalent to the configuration of a mechanical constant estimating device based on an inertial moment estimating operation expression using a sequential least squares method as described in the Institute of Electrical Engineers of Japan, treatise journal, Vol.114-D, No.4, p.424-p.431.
In FIG. 7, reference numeral 41 denotes an acceleration variation signal generating portion for generating an acceleration variation signal da through the signal processing by inputting a machine velocity vm, 42 denotes a torque variation signal generating portion for generating a torque variation signal dxcfx84 through the signal processing by inputting a torque command xcfx84r, 43 denotes a multiplication circuit for calculating the product of the acceleration variation signal da and a previous inertial moment estimated value Je(kxe2x88x921) held in an inertial moment estimated value holding portion 47, 44 denotes a subtracter for subtracting the product of the acceleration variation signal da and the previous inertial moment estimated value Je (kxe2x88x921) calculated in the multiplication circuit 43 from the torque variation signal dxcfx84, and 45 denotes an estimation gain portion for inputting a signal in which the product of the acceleration variation signal da and the previous inertial moment estimated value Je(kxe2x88x921) is subtracted from the torque variation signal dxcfx84 and outputting an error from the previous inertial moment estimated value Je(kxe2x88x921). Also, reference numeral 46 denotes an operating portion for adding the previous inertial moment estimated value Je(kxe2x88x921) to the error output from the estimation gain portion 45 and outputting the inertial moment estimated value Je(k), and 47 denotes an inertial moment estimated value hold portion for holding the inertial moment estimated value Je.
Referring to FIGS. 6 and 7, the operation of the conventional mechanical constant estimating device will be described below. It is assumed here that the driving torque xcfx84m actually produced in the actuator 31 coincides with the torque command xcfx84r.
Supposing that the machine velocity of the drive machine 32 detected by the velocity detector 33 is vm, the machine acceleration am of the drive machine 32 is represented by the following expression (1).
am=sxc2x7vmxe2x80x83xe2x80x83(1) 
In the above expression, s is the Laplace operator.
Also, supposing that the disturbance torque applied to the drive machine 32 is xcfx84d, and the inertial moment (true value) for the drive machine 32 is J, the torque commander xcfx84r is represented by the following expression (2).
xcfx84r=xcfx84d+Jxc2x7amxe2x80x83xe2x80x83(2) 
For simpler explanation, if the torque command xcfx84r is denoted in a continuous time system, and the torque variation signal generating portion 42 obtains a difference between the input torque command xcfx84r at present and the previous torque command xcfx84r, and generates a torque variation signal dxcfx84 from this differential value, the torque variation signal dxcfx84 is represented by the following expression (3).
dxcfx84=sxc2x7xcfx84rxe2x80x83xe2x80x83(3) 
Since the machine velocity vm detected by the velocity detector generally contains the noise component of high frequency, the use of pure differentiation will increase the noise component, causing an estimation error for the mechanical constant. Therefore, the acceleration variation signal generating portion 41 obtains an acceleration variation signal da for the input machine velocity vm by pseudo differential operation having the low pass filter characteristic, instead of pure differentiation. Assuming that the low pass filter characteristic function is F(s), the pseudo acceleration signal af is represented by the following expressions (4) and (5), and the acceleration variation signal da is calculated by the following expression (6).
af=sxc2x7F(s)xc2x7vmxe2x80x83xe2x80x83(4) 
af=F(s)xc2x7amxe2x80x83xe2x80x83(5) 
da=sxc2x7afxe2x80x83xe2x80x83(6) 
If the expressions (2), (3), (5) and (6) are put together, and the low pass filter characteristic function F(s) is ignored as the ideal filter, the torque variation signal dxcfx84 can be represented by the following expression (7).
dxcfx84=sxc2x7xcfx84d+Jxc2x7daxe2x80x83xe2x80x83(7) 
In the expression (7), because the right side first term becomes zero in a steady state where there is no disturbance torque xcfx84d, the inertial moment J can be represented by the following expression (8), whereby the inertial moment J for the drive machine 32 can be estimated as a ratio of the torque variation signal dxcfx84 to the acceleration variation signal da.
J=dxcfx84/daxe2x80x83xe2x80x83(8) 
The mechanical constant estimating device as shown in FIG. 7 employs a sequential least square method in the expression (8) to improve the estimation precision.
Supposing that the inertial moment estimated value at the k-th point of time is Je (k) and the inertial moment estimated value at the previous ((kxe2x88x921)-th) point of time is Je(kxe2x88x921), the operation expression for estimating the inertial moment based on the sequential least square method is shown in the following expressions (9) to (11).
Je(k)=Je(kxe2x88x921)+P(k)xc2x7da(k)xc2x7(dxcfx84(k)xe2x88x92da(k)xc2x7Je(kxe2x88x921))xe2x80x83xe2x80x83(9) 
P(k)=P(kxe2x88x921)/(xcex+P(kxe2x88x921)xc2x7da(k)2)xe2x80x83xe2x80x83(10) 
G(k)=P(k)xc2x7da(k)xe2x80x83xe2x80x83(11) 
In the above expressions, xcex is a constant called a forgetfulness factor, and is chosen to be slightly smaller than one to cope with a change in the inertial moment of the drive machine. Also, P(k) is an estimation gain parameter of one kind provided in the mechanical constant estimating operation, and updated while changing as the acceleration variation signal da is varied in magnitude.
The estimation gain G(K) in the estimation gain portion 45 is represented by the expression (11) including the operation expression (10) for the estimation gain parameter P(k).
If the inertial moment estimated value Je(kxe2x88x921) at the previous ((kxe2x88x921)-th) point of time is a true value, the right side second term of the expression (9) becomes zero, so that the inertial moment estimated value Je is not updated.
However, if the inertial moment estimated value Je (kxe2x88x921) at the previous ((kxe2x88x921)-th) point of time is different from the true value, an error term of torque variation (dxcfx84(k)xe2x88x92da(k)xc2x7Je(kxe2x88x921)) arises with the estimation error, whereby the inertial moment estimated value Je(k) at the k-th point is equal to the sum of the previous inertial moment estimated value Je(kxe2x88x921) at the previous point of time and the error term of torque variation multiplied by the estimation gain G(k), as shown in the expression (9).
While the above discussion is concerned with an instance where there is no disturbance (disturbance torque xcfx84d=0), a moment at which an impact disturbance is applied in the steady state will be contemplated.
Supposing that the torque variation occurring upon an impact disturbance applied in a direction of obstructing the rotation of motor in the steady state is dxcfx84xe2x80x2 and the acceleration variation is daxe2x80x2, employing the expression (9)
Je(k)=Je(kxe2x88x921)+P(k)xc2x7da(k)xc2x7(dxcfx84(k)xe2x88x92da(k)xc2x7Je(kxe2x88x921)) 
the following expression (12) results.
Je(k)=Je(kxe2x88x921)+P(k)xc2x7daxe2x80x2(k)xc2x7(dxcfx84xe2x80x2(k)xc2x7daxe2x80x2(k)xc2x7Je(kxe2x88x921))xe2x80x83xe2x80x83(12) 
When an impact disturbance is applied in a direction of impeding the rotation of motor, the motor is decelerated momentarily, thereby giving rise to a great acceleration variation of daxe2x80x2 less than 0.
On one hand, a disturbance torque variation sxc2x7xcfx84d greater than 0 arises at a moment when a disturbance torque of xcfx84d greater than 0 is applied, and a great torque variation of dxcfx84xe2x80x2 greater than 0 arises to compensate for its torque.
In the expression (12), the error term of torque variation (dxcfx84xe2x80x2(k)xe2x88x92daxe2x80x2(k)xc2x7Je(kxe2x88x921)) rapidly increases because dxcfx84xe2x80x2 greater than 0 and daxe2x80x2 less than 0, and the right side second term rapidly decreases because daxe2x80x2 less than 0, whereby the inertial moment estimated value is erroneously estimated to be a significantly small value.
Since the inertial moment estimated value Je is employed for the auto-tuning of control gain in the torque command generating portion 30, as shown in FIG. 6, if the inertial moment is erroneously estimated, the result has an effect on the gain of control system to make it impossible to produce a torque command to make a desired operation, possibly leading to a worse control performance and an unstable phenomenon such as oscillation of the drive machine.
FIGS. 8A and 8B are graphs showing the relation between the disturbance torque and the inertial moment estimated value in the conventional mechanical constant estimating device. FIG. 8A is a graph showing the characteristic of disturbance torque with respect to the time in the drive machine, and FIG. 8B is a graph showing the characteristic of inertial moment with respect to the time. In FIG. 8A, xcfx84d represents the disturbance torque, and in FIG. 8B, the solid line indicates the true value of inertial moment and the broken line indicates the inertial moment estimated value.
In the conventional mechanical constant estimating device, the inertial moment estimated value is substantially the true value, before the disturbance torque is applied, but the inertial moment estimated value rapidly decreases at the same time when the disturbance torque is applied, resulting in a greater error with respect to the inertial moment true value. After the estimated value rapidly decreases, it takes considerable time to restore the original inertial moment estimated value.
It is demanded that the mechanical constant estimation is employed not only for the conventional cutting machine or robot having a variable load but also for the abutment on the conveyer for stopping the conveyed substance at a desired position by abutting it against the equipment. However, there is a problem that the conventional mechanical constant estimating device cannot be used, if a large impact disturbance is applied to the drive machine, because it is difficult to perform the inertial moment estimation correctly, as described above.
The above phenomenon appears with the typical auto-tuning configuration, as shown in FIG. 6, but is especially remarkable with the mechanical constant estimating device using a recursive operation method such as a sequential least square method, as shown in FIG. 7.
The mechanical constant estimating operation by the sequential least square method can avoid the misestimation of inertial moment by choosing the forgetfulness factor xcex to be a sufficiently smaller value than one and reducing the response of inertial moment estimation. However, if the forgetfulness factor is smaller, the estimating device has a smaller estimation gain, and a lower estimation sensitivity to its input, thereby being less responsive to an abrupt change such as an impact disturbance to have a slower response when the estimated value of inertial moment is different from the true value, resulting in a problem of aggravating the performance of inertial moment estimation.
FIG. 9 is a block diagram of a velocity control system containing the conventional disturbance observer and mechanical constant estimating device. In FIG. 9, reference numerals 31 to 33, and reference symbols xcfx84r, xcfx84d, vm and xcfx84rxe2x80x2 denote the same parts as those of FIG. 6, and their description is omitted. Reference numeral 35 denotes a torque command generating portion, 36 denotes a mechanical constant estimating device for estimating the inertial moment estimated value Je by inputting the machine velocity vm of the drive machine 32 and a torque command xcfx84rxe2x80x2 not containing any disturbance torque component due to impact disturbance, and 37 denotes a disturbance observer for removing the disturbance.
FIG. 9 is to solve the problem associated with the conventional mechanical constant estimating device that the inertial moment estimation is difficult to correctly perform when a large impact disturbance is applied to the drive machine, in which the torque command xcfx84rxe2x80x2 having disturbance removed by the disturbance observer is input into the mechanical constant estimating device to make the mechanical constant estimation without being affected by impact disturbance.
As the torque command input into the mechanical constant estimating device 36, the torque command xcfx84rxe2x80x2 not containing any disturbance torque component due to impact disturbance is employed to make the mechanical constant estimation without being affected by the impact disturbance, but is not practical because there is the risk that the operation becomes unstable due to the interference of the auto-tuning of control system gain by the mechanical constant estimating device and the disturbance removal by disturbance observer, in which there is a problem that the control system is so complex as to make it difficult to grasp the convergence characteristic.
This invention has been achieved to solve the above-mentioned problems, and it is an object of the invention to provide a mechanical constant estimating device that can estimate the inertial moment correctly even when a large impact disturbance is applied to a drive machine.
The present invention provides a mechanical constant estimating device comprising an acceleration signal generating portion for generating an acceleration signal of low frequency by inputting a machine velocity of a drive machine employing an actuator such as a motor, a pseudo torque signal generating portion for generating a pseudo torque signal of low frequency by inputting a torque command and removing the noise, a multiplication circuit for calculating a product of the acceleration signal and a previous mechanical constant estimated value, a torque error signal calculating portion for calculating a torque error signal by subtracting the product obtained by the multiplication circuit from the pseudo torque signal of low frequency, a torque error derivative signal generating portion for generating a torque error derivative signal by inputting the torque error signal, a mechanical constant estimation gain portion for estimating a mechanical constant by inputting the torque error derivative signal, and a mechanical constant estimated value calculating portion for calculating the mechanical constant estimated value by adding the previous mechanical constant estimated value to an error output from the mechanical constant estimation gain portion, wherein the torque error signal calculated by the torque error signal calculating portion is output as a disturbance torque estimated value, and the mechanical constant estimation gain portion starts or stops to update the mechanical constant estimating operation, or changes the mechanical constant estimation gain, on the basis of the disturbance torque estimated value. Therefore, the mechanical constant of the drive machine and a disturbance element acting on the drive machine can be estimated at the same time, whereby the misestimation of the mechanical constant due to the disturbance element and the misestimation of the disturbance element due to a change in the mechanical constant can be prevented.
Also, the mechanical constant estimating device further comprises at least two or more disturbance torque extracting portions having a filter characteristic for decomposing and extracting a frequency component from the disturbance torque by inputting the torque error signal calculated by the torque error signal calculating portion, wherein the mechanical constant estimation gain portion starts or stops to update the mechanical constant estimating operation, or changes the mechanical constant estimation gain, on the basis of the disturbance torque component with the frequency component decomposed that is extracted from the disturbance torque extracting portion. Therefore, the disturbance element of frequency component specific to the machine or the use can be taken out, whereby the misestimation of the mechanical constant due to the disturbance element and the misestimation of the disturbance element due to a change in the mechanical constant can be prevented.
Further, the mechanical constant estimation gain portion stops to update the mechanical constant estimating operation or reduces the mechanical constant estimation gain for a period from the time when a disturbance is applied to the drive machine to the time when a steady state is restored. Therefore, the misestimation of the mechanical constant due to the disturbance element and the misestimation of the disturbance element due to a change in the mechanical constant can be easily prevented.
Further, the mechanical constant estimation gain portion applies a statistical processing method such as a least square method in estimating the mechanical constant of the drive machine, and starts or stops to update the parameter calculation for use in estimating the mechanical constant, or changes the constant, on the basis of the disturbance torque estimated value. Therefore, the misestimation of the mechanical constant due to the disturbance element and the misestimation of the disturbance element due to a change in the mechanical constant can be easily prevented while keeping a high response.
Also, this invention provides a mechanical constant estimating device comprising an acceleration variation signal generating portion for generating an acceleration variation signal by inputting a machine velocity of a drive machine employing an actuator such as a motor, a torque variation signal generating portion for generating a torque variation signal by inputting a torque command and removing the noise, an acceleration variation vector generating portion for generating an acceleration variation vector by inputting the acceleration variation signal, a multiplication circuit for calculating a matrix product of a previous parameter vector estimated value composed of a mechanical constant estimated value and an estimated value of disturbance torque component and the acceleration variation vector, a subtracter for subtracting the product calculated by the multiplication circuit from the torque variation signal to output a torque error derivative signal, a mechanical constant estimation gain portion for estimating an error vector by inputting the torque error derivative signal, and an adder for adding the previous parameter vector estimated value to the error vector output from the mechanical constant estimation gain portion to output the mechanical constant estimated value, wherein the mechanical constant estimated value and the estimated value of disturbance torque component as a pair are estimated as a parameter vector estimated value at the same time. Therefore, the malfunction of estimating the inertial moment due to disturbance torque is prevented and the estimation result of high precision can be obtained.